1. Field of the Invention
Embodiments of the present invention generally relate to a dynamic load lock chamber that is adapted to transfer one or more substrates from a first region that is at first pressure to a second region that is at a second pressure different than the first pressure.
2. Description of the Related Art
There is an ongoing demand for photovoltaic (PV) devices or solar cells to generate electrical power with higher efficiency. PV devices are typically formed on a thin, fragile substrate, which typically comprises silicon, although other substrate materials may be used. As the demand for PV devices continues to grow, there is a trend to reduce cost by increasing the substrate throughput and improving the quality of the deposition processes performed on the substrate. In order to meet these challenges, the following solar cell processing requirements generally need to be met: 1) the cost of ownership (CoO) for substrate fabrication equipment needs to be improved (e.g., high system throughput, high machine up-time, inexpensive machines, inexpensive consumable costs), 2) the area processed per process cycle needs to be increased (e.g., reduce processing per Watt-peak (Wp)) and 3) the quality of the formed layers and film stack formation processes needs to be well controlled and sufficient to produce highly efficient solar cells.
An issue with thin substrates, in particular thin silicon substrates used for solar cells, is enabling high throughput processing while minimizing the breakage thereof. These very thin silicon substrates are also subject to chipping of fracture if they are impacted against an object, and once they are chipped or broken, they cannot be used for solar cell production. Because solar cell production typically includes multiple deposition, printing and annealing steps which are undertaken in multiple independent processing tools, the cost of damaging a substrate increases at each stage in the fabrication process.
One challenge in this regard involves introduction of these substrates from an ambient pressure environment (typically at or near atmospheric pressure) into a low pressure processing environment. Traditionally, this involves moving a batch of substrates through a first slit valve opening, from an environment at ambient pressure into a load lock chamber, which is coupled to, but sealed from, a low pressure processing environment using a second slit valve. The load lock chamber is then sealed from the atmospheric pressure environment using the first slit valve. The pressure is then slowly reduced within the chamber to become at or near that in the processing chamber to prevent unintended, and undesirable, movement of the low mass, fragile substrates which would occur if air currents are produced in the load lock chamber during this pumpdown process. The substrates are then moved into the processing chamber through the second slit valve opening in the load lock chamber. The second slit valve is then closed and the load lock chamber is vented so that it can then receive the next batch of substrates.
However, this traditional load lock transfer process is time intensive and limits the processing capabilities of the entire production line, and thus, increases the cost of producing PV devices. To reduce this cost, while also reducing surface contamination, there is a need for a design of an inventive load lock chamber and process that enables high throughput, improved device yield, reduced number of substrate handling steps, and a compact system footprint.